SSA - DO INLETS NEED JUNCTIONS?

[jamesbarnett]

We are using SSA for the first time, since we didn't know we even had the software until last week, and I have a couple of questions.

1. Do my inlets need a junction with a direct link?

2. How are the sizes of boxes calculated?

[Matt.Anderson · Accepted solution]

James -

No, Inlets are junctions that have a surface inlet component where a connecting pipe can connect either at the surface (drains to inlet) or to the bottom of the catchbasin.

Boxes? I assume you are referring to the actual inlet structure or catchbasin structure.  They are assumed to be 4 foot round, just as Junctions are.

[fcernst]

Do inlets in SSA 2014 allow flooding at their node, or what the SSA manual calls "upwelling flows" shown in the diagrams in the SSA manual?

The previous versions I have tested do not.

[Matt.Anderson]

Fred -

No.  SSA does not support upwelling for Inlets.  Despite the inferance in prior versions of help, SSA functionality does not include reverse flow out of inlet geometry.  SSA 2014 includes a number of inlet capture calculation and gutter spread calculations updates to address reported discrepenacies.

As the inlet calculations support both depth-capture and flow-capture curves, reverse flow in these situations can not be performed. I would suggest to utilize a Junction if you would expect upwelling to occur at an inlet. 

If you desire to have inlet-calculations include upwelling, please feel free to express that desire to product management.

[jamesbarnett]

Matt,

Thanks, I was refering to the catch basin structure.

How can I change the size of the catch basin?

[fcernst]

This is a big problem regarding modeling functionality with SSA....SSA was marketed to us all as having this capability, complete with colorful illustrations showing flooding coming up through an inlet.

Of course you need the ability to have nodes be able to flood and accomodate flow reversals in a Dynamic routing analysis, just like EPA SWMM 5 does.

You can not perform our required dynamic routing dual drainage (sewer and street) analysis with SSA inlets because of this limitation with SSA inlets.

[Matt.Anderson]

James -

For analytics, that option is not available. 

Junctions and Inlets are assumed to be a 4 foot round cyclider for calculation purposes.

If you link the SSA model and the Civil 3D model, I would suggest part matching.

What is the indended purpose of changing the catchbasin size?  Larger? Smaller?  

[jamesbarnett]

The particular model we are working with now 4' is fine.

I found a setting that I thought would make changes, but I can't tell any difference.

Under the Analysis Options ==> Hydrodynamic analysis parameter ==> Junction surface area

[Matt.Anderson]

Fred -

The help document contained an unfortunate colorful image of a structure labeled as an inlet that shows upwelling occuring.  While not intended to cause confusion and frustration for users,  the image was not part of the marketing material nor was intended to champion functionality that has not been designed, developed and tested.  An junction structure in a SSA model (or EPA SWMM model for that fact) can represent an inlet, without the requisite inlet spread calculations that SSA inlets provide.

The image in help has been fixed to avoid any further misconstrued abilities. 

"Of course you need the ability to have nodes be able to flood and accomodate flow reversals in a Dynamic routing analysis, just like EPA SWMM 5 does."

As I indicated in the first response, use a Junction to accomodate that flow reversal, just as EPA SWMM performs. SSA Inlets currently only support Inlet control conditions.  I think I have been consistent in my response to your repeated questions on this issue.  

Might I inquire which jursidition requires dynamic dual drainage routing requirements? 

[Matt.Anderson]

James -

Junction surface area is the area on the ground surface that would flood.  This value is used primarily in a flooded junction.  (Ie, a flooded junction with 100 sf of flooding has less depth than a 10 sf of flooding area)

For On grade inlets - this would not be utilized.  For Sag inlets, if flow reaches an orifice flow depths over your inlet, this may make an effect.  

[fcernst]

"Unfortunate colorful image"  That is incredibly funny to hear now...

I wasn't happy at the time though having to spend time doing my own testing to show you guys the software was not capable of doing this.

Dual drainage analysis:  is used everywhere to analyze existing storm sewer systems.

[fcernst]

Matt,

Let's please take this further now to hopefully help all potential SSA users. I have not tested SSA 2014:

Given that SSA inlets do not allow nodal flooding or flow reversals, what is happening when the maximum depth of the inlet junction is exceeded during a simulation?

1) How is the modeler notified in the results of the flooding that will occur?

2) Does the inlet act as bolted manhole cover, thus creating a pressure head at that location and subsequent pressure flow in the sysytem?

[jamesbarnett]

Matt,

Thanks again.

[fcernst]

...No.  SSA does not support upwelling for Inlets.  Despite the inferance in prior versions of help, SSA functionality does not include reverse flow out of inlet geometry.....

The 2014 SSA manual is still claiming the ability to model system overflows through the storm drain Inlet objects. 

[Matt.Anderson]

Feel free to log a defect that help improperly uses the term overflow.

[fcernst]

Feel free to log a defect that help improperly uses the term overflow.

Why, because you don't feel like it. You want me to burn the calories?

The image below is taken from the Storm Drain Inlets section. It advertises the ability to use the software to  model flow reversals out of the drain inlets for dual drainage anlysis.

Engineer's making purchase decisions based on this information are being misled.

[Sportyyyy]

 

http://forums.autodesk.com/t5/autocad-civil-3d-forum/2015-civil-3d-and-ssa-spacebar-issue/m-p/672522...